Japanese Patent Laid-Open Publication No. 2001-170358 discloses a game system (hereinafter, referred to as “a conventional technique”) using a tilt sensor. In this conventional technique, when a handheld game device or a game controller (hereinafter, referred to as “a game device, etc.” in place of “a handheld game device or a game controller”) is tilted, a game image is generated in which an object such as a player character, etc., moves (rolls over) in the direction of tilt, thereby allowing a player to feel as if a game space is actually tilted in accordance with a tilt of the game device, etc.
The above described conventional technique, however, is used for controlling a two-dimensional game image, and cannot be adapted to a three-dimensional game image which has become prevalent as a game image.